1. Field of the Invention
The invention relates in general to magnetic resonance imaging, and in particular to methods for interventional in vivo magnetic resonance imaging.
2. Related Art
Magnetic resonance imaging (MRI) is a well known, highly useful technique for imaging matter. It has particular use with imaging the human body or other biological tissue without invasive procedures or exposure to the harmful radiation or chemicals present with x-rays or CT scans. MRI uses changes in the angular momentum or xe2x80x9cspinxe2x80x9d of atomic nuclei of certain elements to show locations of those elements within matter. In an MRI procedure, a subject is usually inserted into an imaging machine that contains a large static magnetic field generally on the order of 0.2 to 4 Tesla although machines with higher and lower strength fields are being developed and used. This static magnetic field tends to cause the vector of the magnetization of the atomic nuclei placed therein to align with the magnetic field. The subject is then exposed to pulses of radio frequency (RF) energy in the form of a second, oscillating, RF magnetic field having a particular frequency referred to in the art as a resonant or Larmor frequency. This frequency is equal to the rate that the spins rotate or precess.
This second field is generally oriented so that its magnetic field is oriented in the transverse plane to that of the static magnetic field and is generally significantly smaller. The second field pulls the net magnetism of the atomic nuclei off the axis of the original magnetic field. As the second magnetic field pulses, it pulls the spins off axis. When it is turned off, the spins xe2x80x9crelaxxe2x80x9d back to their position relative to the initial magnetic field. The rate at which the spins relax is dependent on the molecular level environment. During the relaxation step, the precessing magnetization at the Larmor frequency induces a signal voltage that can be detected by antennas tuned to that frequency. The magnetic resonance signal persists for the time it takes for the spins to relax. Since different tissues have different molecular level environments, the differences in relaxation times provides a mechanism for tissue contrast in MRI. The magnetic resonance signal is detected in the form of a voltage that the precessing magnetization induces in an antenna placed nearby.
In order to image the magnetic resonance signal it is necessary to encode the locations of the resonant spins. This is performed by applying pulses of gradient magnetic fields to the main magnetic field in each of the three dimensions. By creating these fields, the location of resonant nuclei can be determined because the nuclei will resonate at different Larmor frequencies since the magnetic field they experience differs from their neighbors. The magnetic resonance (MR) image is a representation of the magnetic resonance signal on a display in two or three dimensions. This display usually comprises slices taken on an axis of interest in the subject, or slices in any dimension or combination of dimensions, three-dimensional renderings including computer generated three-dimensional xe2x80x9cblow-upsxe2x80x9d of two-dimensional slices, or any combination of the previous, but can comprise any display known to the art.
MR signals are very weak and therefore the antenna""s ability to detect them depends on both its size and its proximity to the source of those signals. In order to improve the signal of an MRI, the antenna may be placed near or inside the subject to be imaged. Such improvements can enable valuable increases in resolution sensitivity and reduction of scan time.
Interventional magnetic resonance antennas and coils have been known and used for in vivo examination of organs, tissue, and other biological structures. See, e.g., U.S. Pat. No. 5,699,801 to Atalar et al. However, such devices are not optimized for clinical utility in transesophageal, transtracheal or transbronchial, transurethral, transrectal, transvaginal, intravascular, and other interventional applications because the probes have undesirable mechanical properties, are of incorrect dimension to be useful in these areas, or have not been specifically designed for use in procedures associated with the areas.
It is desired in the art to produce systems and methods for evaluation of anatomic areas. Evaluation of an anatomic area may pertain to normal or abnormal features of the anatomic area. Evaluation of an anatomic area may be undertaken simultaneously with other diagnostic procedures, including those interventional procedures that require insertion of a diagnostic tool within the human body, through a naturally occurring or iatrogenically produced orifice. Evaluation of an anatomic area may be undertaken simultaneously with therapeutic interventions, using techniques for therapeutic interventions well-recognized in the art such as biopsies, excisions, ablations, drug deliveries or other types of local or systemically directed treatments.
It is further desired in the art to produce systems and methods for performing medical interventions, where guidance for the interventions can be anatomically detailed and can further include the entire region of anatomic interest. A medical intervention may be a diagnostic or a therapeutic procedure or some combination thereof. As understood herein, any person who views images produced that represent an anatomic area in order to understand that anatomic area may be termed a xe2x80x9cdiagnostician,xe2x80x9d even though that person is viewing the images for therapeutic as well as diagnostic purposes, and even if that person is viewing the images only to understand the anatomy and not to diagnose an abnormality.
In certain embodiments, the present invention provides systems and methods for the evaluation of anatomy of the mediastinum, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides systems and methods for the evaluation of the pancreaticohepaticobiliary anatomy, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides systems and methods for the evaluation of the tracheobronchopulmonary anatomy, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides systems and methods for the evaluation of the head and neck anatomy, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides systems and methods for the evaluation of the genitourinary anatomy, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides systems and methods for the evaluation of the vascular anatomy, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides systems and methods for the evaluation of the gastrointestinal system, and for diagnosis and treatment of abnormalities therein.
In certain embodiments, the present invention provides methods for evaluating internal fluid collections, for diagnosing and for treating them.
Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.